Experienced observers of the Northern Ireland conflict must feel like the frustrated passengers queuing patiently for the proverbial and highly elusive Number 9 bus. They have waited for more than a quarter of a century for a balanced, erudite and lucid account of the modern IRA and then two arrive in quick succession.

Hard on the heels of Ed Moloney's outstanding Secret History of the IRA comes Richard English's Armed Struggle, another book dealing with the Provisionals' evolution since 1969. But while Moloney's book reads like a le Carré novel, English's history resembles a thematic epic, Tolstoyan almost in tone, with grand ideas and historic concepts explored and sometimes ridiculed over the expanse of 30 years.

The Queen's University professor takes the axe to the roots of modern IRA mythology. Yet he does so at a measured pace, carefully lopping off Provo legends one at a time rather than felling them with one brutal blow. He avoids the hysterical tempo of moral outrage opting, instead, for a calm, rational but in the end devastating deconstruction of the IRA.

He dismisses one of the IRA's foundation myths: that they were the armed defenders of Catholics against loyalist aggression. English admits there was some evidence that in the Provisionals' fledgling months, the IRA beat off loyalists attacking Catholic areas. But he reminds us that republican violence throughout the Troubles actually provoked loyalist counter-violence, with ordinary nationalists the main victims. Yet even after the IRA's most vaunted early success - the defence of the Catholic enclave of Short Strand, east Belfast in June 1970 - English points out that the IRA failed to defend the Catholic community in the city.

Between the Battle of the Short Strand to December 1972, loyalist terror groups and the British Army between them killed 171 Catholic civilians. And when the IRA attempted to deliver a knockout blow to a resurgent UDA in October 1993 and instead killed nine Protestants, the net result was more Catholics killed in retaliation. So much, he says, for the idea that IRA arms could halt sectarian slaughter in the North of Ireland.

English hacks away carefully at a second core IRA myth: that the unionists would stop being unionists once Britain withdrew from Northern Ireland. The author rejects the theory, propagated not only by the Provisionals themselves but also by their supporters on the British Left over the last 30 years, that the 'armed struggle' was somehow a classic anti-imperialist war.

Perhaps that is why so many prisoners and activists walked about with copies of Franz Fanon's Wretched of the Earth shoved into their coat pockets. He is scathing in an understated way of the Provisionals' Third World pretensions, trying to portray Northern Ireland as akin to apartheid South Africa or Algeria under French oppression.

His conclusion is that this 'armed struggle' rested on an entirely false premise. Even within the IRA and Sinn Fein there was the growing realisation as the 'war' ground to its inexorable end that they had 'got the unionists wrong', disregarding their presence as a kind of Irish version of Marxist false consciousness. One of the most fascinating aspects of the book is the admission (albeit too late for their victims) by senior republican figures that their vision of unionists and unionism was myopic and one-dimensional, a hopeful sign perhaps for the future.

The author, while scornful about the futility of the IRA campaign, is balanced in the blame game. He lays much of the responsibility for the Provisionals' endurance on the stupidity of unionist leaderships and (at least in the early years) the bungling brutality of the British armed forces. What made men like Patrick Magee, the IRA bomber who almost wiped out the entire Cabinet, including Margaret Thatcher, at Brighton in 1984? In part, English concludes, it was republican mythology and history. But he argues that Magee and others were also the products of the mean streets where they grew up. In Magee's case, his republican epiphany came about after being maltreated by a British foot patrol near his home.

Correspondents in Iraq have contrasted (maybe unfairly) the gung-ho attitude of American occupying troops to the more subtle approach of British soldiers in Basra. They have concluded that the Brits are better equipped to deal with urban occupation, given their experience in Northern Ireland.

Armed Struggle should be read in Iraq by American and British commanders alike. It provides lessons on how a military force initially welcomed by an indigenous population can, through arrogance and ineptitude, alienate those it had come to protect or liberate.